Buckle is commonly used as a verb to refer to the fastening of a belt or shoe. However, there are a variety of synonyms that can be used in its place. Some potential options include clasp, fasten, snap, secure, and lock. These words all have slightly different connotations, with clasp suggesting a more delicate or decorative fastener and snap indicating a quick and easy way to secure something. Fasten and secure both suggest a strong hold, while lock could be used in the context of a seatbelt or similar restraint. Overall, there are many potential synonyms for buckle depending on the specific context and desired tone.